This application claims Paris Convention priority of Japanese Patent Application No. 2000-021961 filed Jan. 31, 2000, the complete disclosure of which is hereby incorporated by reference.
This invention relates to a metal film/aromatic polyimide film laminate and further relates to a metal film/aromatic polyimide film/metal film laminate.
Aromatic polyimide films show good high temperature resistance, good chemical properties, high electrical insulating property, and high mechanical strength, and therefore are widely employed in various technical fields. For instance, an aromatic polyimide film is favorably employed in the form of a continuous aromatic polyimide film/metal film composite sheet for manufacturing a flexible printed circuit board (FPC), a carrier tape for tape-automated-bonding (TAB), and a tape of lead-on-chip (LOC) structure.
The aromatic polyimide film/metal film composite sheet can be produced by bonding a polyimide film to a metal film using a conventional adhesive such as an epoxy resin. However, due to low heat-resistance of the conventional adhesive, the produced composite sheet cannot show satisfactory high heat-resistance.
For obviating the above-mentioned problem, a variety of bonding methods have been proposed. For instance, an aromatic polyimide film/metal film composite sheet is manufactured by producing a copper metal film on an aromatic polyimide film by electroplating. Otherwise, an aromatic polyamide solution (i.e., a solution of a precursor of an aromatic polyimide resin) is coated on a copper film, dried, and heated for producing an aromatic polyimide film on the copper film.
An aromatic polyimide film/metal film composite sheet also can be produced using a thermoplastic polyimide resin.
U.S. Pat. No. 4,543,295 describes a polyimide laminate which is produced by applying a pressure onto a composite sheet composed of an aromatic polyimide film, a polyimide adhesive, and a metal film in vacuo.
In most of the known metal film/aromatic polyimide film laminates, the bonding between the metal film and the polyimide film is satisfactorily high. However, it has been found by the present inventors that a metal film having a smooth surface, such as a stainless steel film having been not subjected to surface roughening treatment, shows poor adhesion to the known thermoplastic polyimide film. The stainless steel film having smooth surface is employed, for instance, in the form of a stainless steel film/aromatic polyimide film/copper film laminate as a part of a slider/suspension assembly for data recording disc system.
It is an object of the invention to provide a metal film/aromatic polyimide film laminate in which a metal film is bonded to an aromatic polyimide film at a high bonding strength, even if the metal film has a smooth surface.
It is another object of the invention to provide a metal film/aromatic polyimide film/metal film laminate in which each metal film is bonded to an aromatic polyimide film at a high bonding strength, even if one of the metal films has a smooth surface.
The invention resides in a metal film/aromatic polyimide film laminate comprising a metal film and an aromatic polyimide substrate film, which are combined with each other by an intervening amorphous aromatic polyimide film of 0.05 to 3 xcexcm thick which has a glass transition temperature in the range of 200 to 300xc2x0 C.
The invention also resides in a metal film/aromatic polyimide film laminate comprising a metal film and an amorphous aromatic polyimide film fixed onto the metal film, the polyimide film having a thickness of 0.05 to 3 xcexcm and a glass transition temperature of 200 to 300xc2x0 C.
The invention also resides in a metal film/aromatic polyimide film/metal film laminate comprising a first metal film, an amorphous aromatic polyimide film of 0.05 to 3 xcexcm thick which has a glass transition temperature in the range of 200 to 300xc2x0 C., an aromatic polyimide substrate film, and a second metal film, in order, in which the substrate film has a thickness of 10 to 150 xcexcm and a linear expansion coefficient of not higher than 30xc3x9710xe2x88x926 cm/cm/xc2x0 C. in the temperature range of 50 to 200xc2x0 C., and comprises a non-thermoplastic polyimide base film and a thermoplastic polyimide layer fixed onto each surface of the base film.